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If (S_n+S_{n-1}=400) and (S_n-S_{n-1}=20), what is (S_n)?
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Answer and explanation
Correct answer: (210)
Adding the two equations gives (2S_n=420), so (S_n=210). When two equations are given, addition is quick.
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What is the correct answer to this question?
(210)
Why is this the correct answer?
Adding the two equations gives (2S_n=420), so (S_n=210). When two equations are given, addition is quick.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: Sum of first n natural numbers.
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